java - QueryDSL 按计算字段排序

Question

在我们的应用程序中，我们使用 querydsl 来获取实体并将它们转换为表示对象。该表示对象具有名为active 的字段。这是由实体的某个日期是在今天之前(active = false)还是在今天之后(active = true)决定的。这样做一切都很顺利。问题是当尝试按该表达式(QEntity.someDate > Today)进行排序时。这使得 hibernate 抛出此错误:

org.hibernate.hql.internal.ast.QuerySyntaxException: unexpected AST node: > near line 3, column 40 [select object.someField as someAlias, (object.someDate > ?1) as active, object as objectAlias
from com.example.Object object
order by object.someDate > ?1 asc]

我创建 OrderSpecifier 如下:

    @Override
    public OrderSpecifier<?> getOrderByClause(SortKey sortKey) {
        BooleanExpression expression = getBooleanPath(); // This is the expression: (object.someDate > ?1)
        if (sortKey.getSortOrder() == ESortOrder.ASCENDING) {
            return new OrderSpecifier(Order.ASC, expression);
        }
        return new OrderSpecifier(Order.DESC, expression);
    }

我也尝试过这样的:

    @Override
    public OrderSpecifier<?> getOrderByClause(SortKey sortKey) {
        BooleanExpression expression = getBooleanPath();
        if (sortKey.getSortOrder() == ESortOrder.ASCENDING) {
            return new CaseBuilder().when(expression.isFalse()).then(1).otherwise(2).asc();
        }
        return new CaseBuilder().when(expression.isTrue()).then(1).otherwise(2).desc();
    }

这会导致类似的错误:

org.hibernate.hql.internal.ast.QuerySyntaxException: unexpected AST node: > near line 3, column 40 [select object.someField as someAlias, (object.someDate > ?1) as active, object as objectAlias
from com.example.Object object
order by case when (object.someDate > ?1 = ?2) then ?3 else 2 end asc]

最后是这样的:

    @Override
    public OrderSpecifier<?> getOrderByClause(SortKey sortKey) {
        BooleanExpression expression = getBooleanPath();
        if (sortKey.getSortOrder() == ESortOrder.ASCENDING) {
            return new CaseBuilder().when(expression.eq(true)).then(1).otherwise(2).asc();
        }
        return new CaseBuilder().when(expression.eq(true)).then(1).otherwise(2).desc();
    }

这会引发与之前相同的错误

Answer 1

通过创建如下所示的 order 子句来修复它:

    @Override
    public OrderSpecifier<?> getOrderByClause(SortKey sortKey) {
        BooleanPath path = getBooleanPath();
        if (sortKey.getSortOrder() == ESortOrder.ASCENDING) {
            return path.asc();
        }
        return path.desc();
    }

    private BooleanPath getBooleanPath() {
        return Expressions.booleanPath(getFieldName());
    }

其中字段名称是字符串形式的别名，在我们的例子中为“active”。